There is known an industrial robot system which includes a robot provided with an end effector such as a hand at the end of an arm via a force sensor. In this kind of robot system, in the case of the robot performing assembly of parts, a force or a moment component generated at a wrist portion at the time of an assembly operation is detected by the force sensor, to control a posture of the robot including the hand.
At the manufacturing stage of a force sensor, variations in output with respect to an external force occur, and hence the output needs to be corrected. Therefore, when the sensor is a six-axis force sensor, respective axes, such as forces Fx, Fy, Fz and moments Mx, My, Mz, are provided with a force by means of weights or the like, to perform correction based on the outputs. This corrected force sensor is mounted on the arm and used.
Meanwhile, when the robot mounted with the force sensor is in use, an excessive load may be erroneously applied, to cause occurrence of plastic deformation or the like, thereby leading to lower measurement accuracy. In that case, what has been done is to temporarily remove the force sensor from the arm and perform a re-correction operation, which requires time and trouble. As opposed to this, there has been proposed one that corrects a force sensor in a mounted state. For example, in Japanese Patent Application Laid-Open No. H11-237296, In PTL 1, first, reference data is previously acquired when the force sensor is normally functioning. Then, when the force sensor needs to be corrected, the correction is performed such that a posture of a robot is changed in a predetermined pattern, thereby to change a posture of the force sensor and obtain a changed amount of an output signal of the force sensor, which is compared with reference data and then updated. It is described that by the above manner, the correction can be performed with the force sensor remaining mounted in the robot.
However, in the foregoing conventional correcting method, the reference data needs to be acquired beforehand. Further, there has been a problem in that, when an end effector provided at the end of the arm is not the end effector at the time of acquiring the reference data, the end effector has to be exchanged, which requires time and trouble.
In recent years, a robot system provided with a pair of robots set so as to perform collaboration work has been proposed and a method for correcting a force sensor in a simpler manner in the case of a large number of robots has been desired.
Therefore, an object of the present invention is to provide a force sensor correcting method which is simple and capable of performing correction, with the force sensor remaining mounted at the end of an arm without an exchange of an end effector.